In the most recent quarter century, there has been a major effort to increase fuel economy of automotive vehicles. To achieve an increase in fuel economy, several technical trends have developed. One technical trend is a change from rear wheel drive to front wheel drive vehicles. Front wheel drive vehicles tend to increase fuel economy by placing the weight of the engine over the traction wheels of the vehicle. Another technical trend is to diminish the vehicle's aerodynamic drag. To lower the aerodynamic drag, the hood region of many vehicles has been lowered. The front end of the vehicle is more round or pointed instead of the box front end which was common on many prior vehicles. Additionally, the grill area is typically smaller.
The use of two-stroke cycle internal combustion engines has been proposed to significantly reduce vehicle weight and to further reduce aerodynamic drag by further lowering the hood. Conventional two-stroke internal combustion engines have a very high power-to-weight ratio. Accordingly, use of a two-stroke engine would reduce the overall vehicle weight. Moreover, two-stroke engines have a very high power-to-space ratio as compared with the conventional four stroke engines. Accordingly, the use of two-stroke engines would allow for further lowering of the front hood to further reduce the aerodynamic drag of a vehicle.
Conventional two-stroke engines have been limited in their applications by issues with symmetrical port opening control times and, as a result, short circuit scavenging. To reduce the port opening control time, scavenging pumps are employed to overcome the limitations of scavenging at gage pressure. Limitations in available economic sealing methods effectively limit pump pressure and therefore the volumetric efficiency of the engine. Thermo-efficiency is also limited by the need to keep incoming air dense (cool).
It is desirable to provide a two-stroke internal combustion engine which provides a high scavenge pressure that delivers high density air and also reduces the port opening time.